The present invention relates to a neutral particle analyzer for performing mass analysis, energy analysis, and detection of particle numbers of electrically neutral particles, for example, neutral hydrogen particles.
More studies have been recently made on nuclear fusion. Nuclear fusion is defined as a fusion reaction of deuteron (D.sup.+) or triton (T.sup.+) in a plasma at ultra-high temperatures. Particles such as H.sup.+, D.sup.+, T.sup.+ and electrons are present in the plasma. However, H.sup.+, D.sup.+ and T.sup.+ are recoupled with electrons to produce electrically neutral H, D and T. It is possible to determine the ion density or temperature in the plasma by extracting these neutral particles from the plasma and by analyzing or detecting the mass, energy or particle number thereof.
An apparatus as shown in FIG. 1 is conventionally known for analysis of neutral particles. Referring to FIG. 1, a charge exchanging section 1 comprises a vacuum envelope 2; a stripping cell 3 arranged inside the vacuum envelope 2; a gas supply source 4 for feeding nitrogen gas or hydrogen gas to the stripping cell 3; and a vacuum pump 6 for evacuating the gas inside the envelope 2 through evacuating parts 5a and 5b formed at the envelope 2 so as to keep the interior of the envelope 2 at a vacuum of high order. A momentum analyzer 7 is arranged in the proximity of the charge exchanging section 1 of this apparatus. The momentum analyzer 7 comprises a magnet for inducing a magnetic field which is perpendicular to the path of positive particles from the charge exchanging section 1. A plurality of energy analyzers 8a to 8e is arranged in the path of the positive particles from the momentum analyzer 7. Each energy analyzer comprises a pair of concentric arc-shaped electrode plates 14s and 14t, and a power source (not shown) for applying a voltage to these electrode plates 14s and 14t. The radius of curvature of the electrode plates differs from one energy analyzer to another. Ion detectors 9a to 9e are arranged at later stages of the energy analyzers 8a to 8e in correspondence therewith. These ion detectors 9a to 9e generate pulse signals corresponding to the number of charge particles received. The atmospheres around the momentum analyzer 7, the energy analyzers 8a to 8e, and the ion detectors 9a to 9e are evacuated by the vacuum pump 6.
With a conventional neutral particle analyzer of this configuration, the measurement of the neutral particles is performed as follows.
A neutral particle beam 11 which becomes incident on the charge exchanging section 1 is converted into a positive charged particle beam 12 with the orbital electrons removed but with the momentum and kinetic energy of the individual particles remaining constant. The positive charged particle beam 12 then becomes incident on the momentum analyzer 7 which deflects the particles with radii of curvature proportional to the momenta of the individual particles and which produces particle beams 13a to 13e emerging on different paths.
Taking the particle beam 13a which is deflected with the smallest radius of curvature as an example among the particle beams 13a to 13e, this particle beam 13a consists of particles which have the same momentum but which have different energies according to their particle masses. If the particle beam 13a contains protons (H.sup.+), deuterons (D.sup.+) and tritons (T.sup.+), these particles will have the same momenta. Therefore, the energy of the deuterons is 1/2 that of the protons and the energy of the tritons is 1/3 that of the protons. In order to analyze particles of the particle beam having different particle energies, it is necessary to select a suitable voltage to be applied to the energy analyzer. Let r.sub.in and r.sub.out denote the radii of curvatures of the electrode plates 14s and 14t of the energy analyzer 8a, and let -V and +V denote voltages applied to the electrodes 14s and 14t; the energy E of the particles which pass through the energy analyzer can then be expressed by equation (1) below: EQU E=qV/ln (r.sub.out /r.sub.in) . . . (1)
where q is the charge of the incident charged particles. As may be seen from equation (1) above, the energy of the particles analyzed is proportional to the voltage applied to the energy analyzer provided that the radii of curvature r.sub.in and r.sub.out of the electrode plates 14s and 14.sub.t have predetermined values, that is, provided that the energy analyzer has a predetermined shape. Therefore, in the case of energy analysis of a particles beam containing particles proton, deuteron and triton, it is possible to perform energy analysis of the particles which have the same momentum but different masses by sequentially applying, in stepped forms, a voltage 15 which allows the passage of tritons, a voltage 16 which allows the passage of deuterons, and a voltage 17 which allows the passage of protons, as shown in FIG. 2.
In this manner, energy analysis of charged particles having different masses may be accomplished by guiding the particle beams 13a to 13e having different momenta from the momentum analyzer 7 to the corresponding energy analyzers 8a to 8e, and applying voltages, corresponding to the energies of particles having different masses, to the electrodes of the respective energy analyzers 8a to 8e, as shown in FIG. 2.
The particles which pass through the energy analyzers 8a to 8e then become incident on the ion detectors 9a to 9e which produce electric signals. In order to count the number of every type of particles, the ion detectors conveniently comprise secondary electron multiplier. In order to measure the energy intensity, the ion detectors conveniently comprise Faraday cups.
With a conventional neutral particle analyzer, the voltage to be applied to the energy analyzer must be varied to correspond to the mass of the particles to be analyzed as described above in order to obtain the energy distribution of the neutral particles having different masses. Therefore, the analysis time of the desired particles having a specific mass in the total analysis time is limited. Moreover, it is impossible to perform the simultaneous measurement of the energy distributions of the particles having different masses. Since the energy analyzers are large in size and must be arranged in arc-shapes, the number of analyzers which may be used is limited due to spatial factors. This results in a disadvantage of low energy resolution.